Visible Light / Near UV curable resins

It's been a long time since I posted here and I am coming back with some results and a question to the community:

I have been researching within another 3D printer group on resins to be activated with regular visible light in the blue spectrum range, together with some near UV. This is the spectrum emitted by regular halogen lights form DLP projectors and also some unprotected Tungsten incandescent bulbs of the kind you find in the car lamps or home illumination.

These resins for this currently available in the market, on the other hand, go around 150 to 300$ per kg range. They are hugely expensive and are mostly used for stereolythography 3D printing, such as Envisiontec. Quite a lot of exciting and successful work has been done to make a DIY printer with 0.05 to 0.2mm pixel accuracy. But the cost of the resin that is able to cure at those wavelengths at low wattage in a time frame within the seconds remained a potent deterrent.

Tinkering around with resins and photoinitiators I have now achieved some formulations that are way cheaper from what is out on the market. How much cheaper? Well that depends on how much bulk I can buy, but I can already guaranty less than half the price, probably even lower. Can I go below that price, like reeeeealy cheap?
The answer is yes, sure! But not if I have to invest blindly into a metric ton of the stuff without knowing that I'm going to be able to get it off my hands.

I am able to do this with Acrylic resins, clear and color, with fillers.
I'm also working on Polyester for even cheaper resins, although shrinkage there is more of an issue.
Epoxy may also come along.

The question I have for you people: how many people are actually interested in such resin material?
I know that here in RepRap you have people that work with syringe dispensers and that would welcome a material that can be cured in seconds after dispensing with non-dangerous, regular light source of low wattage.

Nice to encounter some friendly faces over here again!
You seem to have an interesting setup. The LEDs you are using, if collimated enough may very well work with the formulations I am thinking of delivering. Each will work with a different one, as I will be using two different Photoinitatiors.
I'm currently documenting my work over at [3dprinter.wikidot.com]
When I find some time I will try and duplicate my posts over there here in the RepRap forum or wiki if allowed. I know there are very capable people here that would be interested.

I'm currently looking to create a crowd-funding project over at indiegogo (I'm in Europe, so kickstarter is not possible) to get some sort of pre-order setup to raise part of the funds I would need to buy base materials in bulk.
I'll post that here as well once I'm done.

For laser-sintering powder i'm mostly using infrared diode lasers with 808nm or 975nm and output powers with 5, 9 and 25 Watts, what's enough energy for materials like dark plastic, brown lignin, dark ceramics and metal (then with inert gas). But i achieve best results with a 50Watts fibre laser with 1070nm.

When combining the IR-lasers with weak blue or UV diodes, we can change the fabbing material during a session from different dusts to light-curing pastes, that can be applied locally with a syringe and cured selective and then removing the not cured residues and continue with powder sintering ... or start with the liquids and embedd sintered parts ...

I'm trying to make complex 3D-modules made from ceramic, plastic or wood (lignin) with metallic (conductive) parts inside

I would certainly be interested in an inexpensive visible-light curable product. It is the possibility of printing very high resolution objects that makes it attractive. However, at the moment I cannot envision any realistic scenario where I would want more than a couple of liters a year.

Well this is exactly how I imagine the "market" will be. There will be a "long tail" of users that need small quantities of the resin. And those users need a place where they can get that amount of resin without having to spend $2000 for a pail of it that they won't use in years.

You are right about the very high resolution: we can currently start at 0,05mm voxel resolution.

I am considering waiting to launch my crowd-sourcing project in September, as the summer months are not ideal for these endeavours.

Be sure to show people a way of or have a way of keeping the visible light cured resin away from enough light until it is deposited by the printer. Otherwise you're going to get complaints that their container of liquid resin turned into a solid block of resin or kept clogging the dispenser since it started curing before is was dispensed.

I've been considering sending some resin fomulas to China so that they can start mass producing photo cured resins and low cost machines to flood the market. It's all a race to the bottom anyway.

I am very interested in the material you tell about... you see I got my own Envisiontec Ultra but the resins are so expensive that it is impossible to earn any money at all... so now the machine is simply not running - or very less...

I have 2 envisiontec machines and also Meiko LCV-700 SLA machine that also operates on 405nm.
Especially meiko resin is hard to get and cost over 600,-USD per kg.
I also do not need a wax filled resins - no direct metal casting.

I'm able to order a batch of materials or I'm able to buy prototypes of material for testing or participate in development.

For my models I need the best resolution and thin layers. But I may test any resins that cure on 405nm.

Anyone that can sell me the material or point me to someone that can do so, please contact me.
email: silhanek(at)cmkkits.com

I have been discussing with Viktor (VDX) some of the details of the Visible/Near UV light polymerizing resins that i'm sending him. As we were responding through a series of private messages, we realised that this info was better to be found in the public forum, so here it goes:

Spota:
I have prepared the smaples with the H-Nu470 PI, let's see how this works with 445nm
What is the experiment you intend to do? Just blast the laser at a petri dish with the resin?
What exposure times will you test? Be sure not to evaporate the resin, ramp up the power little by little.
And tell me what your results are, I'm eagerly awaiting

Viktor:
Hi Fernando,
my plan was to set a dish filled with a thin layer of polymer on my CNC-mill with equipped 445nm-diodehead and draw some lines starting with nearly no energy and then rising the energy until it starts hardening.
I think it's reacting with light from normal lamps and tubes too?
For best precaution i'll switch to red high-power LED's as ambient light - this should be inactive for the polymer?

Spota:
Exactly, you should avoid any source of blue- light while the resin is exposed.
we use Amber or red light, or a shileding box made of amber plexiglass.

As for the resin depth, there is an issue due to air Oxygen. You may remember us talking about this in another instance. To overcome this, there are several ways:
1) Increase the resin layer depth (>6mm) and shine through the bottom
2) Increase irradiance power
3) Cover surface area with Argon or Nitrogen. Careful with spontaneous polymerisation!

your probes arrived today!
Can you give me some more infos regarding them?
There was some leakage, so I had to throw away the box - should be enough of the fluids left to work with.
I'll try some ideas with the 445nm-diodelaser and 405nm-LED's next weekend ...

All three resins are activated bu the H-Nu470 photoinitiator which has a maximum absorption at 470nm
[3dprinter.wikidot.com]

This system requires quite a high amount of irradiance (W/surface area) to cure and will probably also require a secondary cure process in the sun or with a UV rich light source to cure completely. I think this is the best candidate for curing with lasers at 445nm but this is completely experimental at this moment.

... i think all th bottles have 50% or more of fluid left, so shouldn't be a problem to test the resins.

On Saturday i've wrecked my right hand (surgery is timed for tomorrow), so it's a bit complicated with fine-tuning, but i'll try with the 445nm-diodelaser and aftercuring with the 405nm(?) UV-LED's I've used for Acrifix192 and Bondic-UV-glue ...

This is Junior Veloso's famous blog.
He was not the first to use the DLP technology in the DIY world, I think. There was a previous article form the Univ. of Illinois. But he was the first to get these great results from his equipment and he helped reverse engineer Envisiontec's professional equipment. He managed to boost resolution and with the help of the community over at [tech.groups.yahoo.com] could resolve many of the issues that were still making this design unworkable.

Sometime along the way he decided that he was successful enough and his machine good enough to plan to produce a kit to be sold in a business that he has yet to launch. It should happen within the next few months. But as you said yourself, his blog is short of details and that's because he has little by little been removing all the previously published material, some of which had been developed in an open source fashion. He also mentioned that he was to patent some of the ideas that he had implemented in his design. I don't know if that has been done yet or if he was successful.

Anyway, other people have taken over the open-source documentation in the above mentioned group (see [3dlprint.com] [johns3dp.blogspot.com] [www.chemshapes.com]) some of which are very close (days away) to start printing. I for my part may well wait until Junior has finished his kit and buy one from him. His machine seems to be really nice and well built and I am more of a resin guy than an electrical engineer. It will depend on the price of course.

From what I've seen the right word appears to be "well-configured". I, of course, don't know how much electronics there is in that printer, but it really seems to mostly just be a projector and a stepper motor with the right configuration/software.

I don't know all that much about resin prototyping, but the actual process seems pretty straightforward, get a projector to shine light on a thin layer of raising, as precisely as possible for the right amount of time, raise the plate slightly, repeat.

I'll be the first to admit though, I don't know a whole lot about resin printing and I've just come accross the technology recently then done a bit of research. It's lame that he took down all the collaboratively worked out information, but if people have read it it shouldn't be that much of a problem, since the info is still "there". I can't even really imagine what's there to patent, since resin printers have existed for a long time now, but again I'm not familiar with the subject at all, yet.

I'll take a look at those places, the prospect of building a resin based printer seems really attractive to me

I did think the most complicated part would be making a good/affordable resin mixture. I guess that's because it's much harder to brute force (without chemical knowledge, that is) than some sort of primitive set-up using a projector.

Where is the German CNC forum? I'm fine with german language so I'd love to take a look.

Heheh, I will have to dig up my German too and go through that forum.
Thanks for the info!

Today I received several packages with resin samples and a spectrophotometer. I guess you could call these my christmas present
To bad the spectro is for 110V and the transformer is still due to arrive!! I can't wait!
Now that I have these samples I am fairly confident that I will be able to closely match the commercial resins, good enough to replace a vat full of it without any differences. But on top of that, I would be able to make several different resins with varying flexibility, hardness, toughess, stiffness, filled unfilled, clear...

Next challenge: wax resins that allow for melting and burnout for the investment casting process.

Actually doing what you describe would be even easier with a visible light curing resin. Imagine not having to have any dangerous-over-long-exposures UV light, with resins that have a wide palette of properties, all curing with the output of standard HDI or Tungsten Halogen spotlights [www.google.com] [www.google.com]. I have even cured some of my resins with a regular 50W GR10 spotlight, although some post-curing with harder light (e.g. Sunlight) is then required.

One thing to master is the viscosity of the resin so as to ensure that the thread maintains it's integrity while the resin cures. But I have 2 resin additives that would help me go up or down in viscosity as much as needed.

How is the syringe dispenser or nozzle jet development going on at RepRap?

You can use PIs that only work in a given range of the visible spectrum that you can shield against. This way, you can observe your printing progress through a tinted glass or plexiglass sheet.

Using syringes for viscous or thyxotropic resins is problematic as you don't have a proportional response to actuation and extruded volume. A lot of tweaking would probably be necessary for achieving high precision.

A system using spray nozzles with a low viscosity resin would be a nice solution to try, as there seems to be problems getting ink-jet print heads for an opensourced DIY application (see [forums.reprap.org])

I'm not sure what issues you have been facing with syringes or inkjet, I don't have problems with either. But I decided to make some 385-390nm UV cured photopolymers with a few different monomers and oligomers. They have different viscosities with various strengths and weaknesses.

I'll post the Howto on modifying a low cost DLP for use with a low cost UV LED array. DLP + UV LED's for under $500. I'd like to find a low cost source of DLP projectors. I found a few on closeout for under $100 @ 720p. DLP will print faster than a micro-nozzle array or syringe.

The first design will move in the z-axis only. If I get around to it I'll have the UV projection scan a larger area using a x-y stage. Or I'll leave it up the other devs to expand the design.

EMC2 is probably overkill for the motion controller. Maybe just a PC for video out to the DLP and USB to drive a stepper and limit switches since it's not a realtime application. Project the image onto resin, blank screen, step z, project image, .....wash rinse repeat.

For example, going UV with DLP has some serious deterioration problems with the DMD chip in regular DLP projectors.
Their life expectancy shrinks remarkably once you start removing UV filters inside and bombarding the chip with that kind of radiation. It makes some kind of deposited protection layer vent some nasty volatiles that eventually disrupt it's functioning.

This is one example of the info you may get over at that group. I'll try and have a go at Freenode IRC #reprap soon, maybe make myself more conspicuous here at reprap